<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .container {
          width: 100%;
          height: 100%;
          position: fixed;
          left: 0;
          top: 0;
          display: flex;
          align-items: center;
          justify-content: center;
          background-color: skyblue;
        }
        /*关闭按扭*/
        .container-close {
          background-color: #ddd;
          border: 1px solid #333;
          position: absolute;
          right: 16px;
          top: 16px;
        }
      </style>
</head>
<body>
    <div class="container">
        <!-- The close button -->
        <button class="container-close">X</button>
        <!-- 菜单 -->
        <ul>
          <li>菜单1</li>
          <li>菜单2</li>
          ...
        </ul>
      </div>
</body>
</html>